Such water supply systems in an aircraft have a main supply tank, a plurality of tap lines or pipes connected to a main supply line which in turn is connected to the water supply tank through a pump. The discharge end of each tap line is normally closeable by a valve or faucet and a pump is connected to feed the water from the tank into the main supply line.
German patent Publication DE 4,202,719 A1 (Frank) corresponding to U.S. Pat. No. 5,261,440 (Frank) discloses a water supply system for an aircraft. The Frank system has a main water container and a water displacement container near each faucet. The water is continuously transported back and forth between the supply container and the displacement containers to prevent freeze-up. The water flow is under the control of a valve system which permits supplying compressed air to the water displacement containers or for permitting a back flow operation, whereby compressed air is removed from the water displacement containers. Such a system is capable of sustaining the main water circulation very efficiently. However, tap lines still can freeze-up unless they are separately heated or otherwise connected to a heater to prevent water freeze-up.
German Patent Publication DE 4,227,518 A1 (Ellgoth et al.) corresponding to U.S. Pat. No. 5,303,739 (Ellgoth et al.) discloses a fresh water supply system for an aircraft in which a main tank and auxiliary tanks are so interconnected and under the control of a valve system which operates in such a way that the main line is filled with water only during first time durations while being filled with air during second time durations. A venting valve is connected to the main line to permit the venting of the main line when water is removed from the main line. Air also escapes through the venting valve when the main line is being refilled with water. Tap lines are also periodically emptied by connecting the tap line to a source of reduced pressure through a respective valve. Such a system operates energy efficiently, however, it does not provide water at certain times unless the auxiliary tanks are provided near the taps. Further, auxiliary heating devices are also used in the known system.
There is room for improvement in water supply systems for aircraft with regard to tap lines that hold standing water as long as no water is being taken from the tap line. The use of heating elements is undesirable due to the additional use of energy. The use of a separate circulation in each of the tap lines is also expensive because the tap lines must be constructed as double lines to sustain the circulation. The use of an auxiliary tank for each tap line also leaves room for improvement.